Portal cranes having a pair of legs travelable on generally parallel rails and spanning material storage areas are well-known. The demand for portal cranes has been toward increased capacity cranes which has presented various difficult problems in their manufacture and operation. As a result, heights, spans, and speed of operation of portal cranes have increased to thereby permit higher stacking of material, larger storage areas spanned by the crane, and faster lifting, transporting and lowering of material handled by the crane. However, the increased height and spans have required larger crane frame and leg members, additional wheels, and an increase in size of various other components such as motors and brakes. The larger frame and leg members have a negative effect on the capacity of the crane from the point of view of efficiency in that they increase the mass of the crane and thereby reduce the load carrying ability of the crane for its size. Further, the larger crane members present shipping problems in that railroad car sizes and clearances cannot readily handle the larger members. The solution to this problem has been to divide the crane members during manufacture into smaller sections which can be more easily shipped. This, of course, makes both manufacture and assembly in the field more costly.
The capacity of the portal crane to access a greater amount of material can also be increased by increasing the length of the storage area along which the crane travels. However, this creates a problem with the cable system for supplying electrical power to the crane. A longer storage area and thereby a longer travel distance causes a greater voltage drop in the correspondingly longer electrical power cable. Thus, a longer cable as well as a larger diameter cable to avoid the voltage drop is necessary. The cable is carried on a reel located at the center of the travel run of the crane and is payed out as the crane moves in either direction away from the center and taken in as the crane moves toward the center. As the crane passes the center of the run, the reel has to stop taking cable in, a cable guide has to change its position to pay cable out in a different direction, and the reel has to reverse its rotation direction to pay cable out. This operaiton of the reel becomes extremely difficult to reliably accomplish as the reel diameter increases to handle longer and thicker and thereby stiffer cable, and the travel speed of the crane increases.